There are actually two ways to get filters onto the 80mm Hasselblad lenses (and all 'blad lenses for that matter). The Bay 50 or Bay 60 mounts are the sizes for the internal mount for either the C/C T* or later CF lenses respectively. The lenses also have an option to mount an external bellows style lens hood which is capable of holding gel style filters of various sizes. This allows you to effectively mount any kind of translucent plastic filter in front of the lens properly.

Just for the sake of completeness the Hasselblad has no thread size per say as the Bay system is short for bayonet. The filters are held in via a single notch that is engaged with less than a quarter turn.

The exception to the above answer is the 50mm lens which takes drop in Series 8 filters and requires an included mounting ring.